Swing pressure adsorption process is a technique widely used for separating and purifying of gas mixture in chemical, petroleum and metallurgical industries. It is well known that a specific adsorbent can selectively a adsorb specific gas at an elevated pressure and release it again by depressurization. SPA process provides means for separating and purifying a multicomponent gas stream containing at least two gases having different adsorption characteristics. For example, it may be desired to remove carbon monoxide, carbon dioxide and light hydrocarbons from a hydrogen-containing feed stream to produce a purified hydrogen stream for a hydrocracking or other catalytic process where these impurities are highly adsorbable gases while the hydrogen is less adsorbable.
A set of SPA equipment generally comprises a plurality of adsorption beds filled with adsorbent. During operation, each adsorption bed works sequentially and cyclically as: pressurizing, adsorbing, cocurrent depressurizing, counter-current depressurizing, and purging at a predetermined programme. For different adsorption beds, sequences of process are staggered so that the intermittent operations of different beds constitutes a continuous operation of a SPA equipment.
Generally, the above-mentioned operation is carried out by a programmable control and operation equipment incorporated with the SPA equipment.
The prior art of SPA equipment is widely equipped with computer, pneumatic driving device and ordinary pneumatic operated valves; and others are equipped with computer, electrical driving devices, and ordinary electric operated valves. The general existing problems in valves are low reliability, low hermetization, and short life. In De. Meyer's U.S. Pat. No. 4234322, in case any valve defect happens, the defected valve and its corresponding adsorption bed would be isolated from the system, and the remaining beds will be operated according to a new mode. Such treatment can avoid the whole set from shut down at the sacrifice of the output. Besides, as shown in FIG. 1 of the Patent, all the nine adsorption beds use the same valve (No. 101) to pressurize the product gas. Thus, should this valve fail, the whole unit would have to be shut down. As shown in Publication No. CN 1031660A in the name of Union Carbide Corporation of USA, it describes a modified system of the ordinary SPA process. In this system, the reliability is improved by elimination of several valves, including a system-dependent valve. However, in case that when a valve is in fault, it will still cause the whole or part of the SPA equipment to be shut down.
From the above mentioned patents, it is shown that none of them has attempted to improve the operation stability and reduce the occurrence of defect of the whole SPA process by means of improving the reliability and life of their programmable control and operation devices.